Is there (or does anyone have) a query that will give up the user with the most posts in the last 1 day / 3 days or 7 days..?
(or the equiv. in hours?)

There is a mod at UBBDev if I remember correct that will adjust the top poster island to last "x" days. You can steal the query of that one.

edit: http://www.ubbdev.com/forums/ubbthreads.php?ubb=showflat&Number=312682

you can also limit the top poster from that list, if they are such a post whore as to not mean much in the list. i think someone asked for that somewhere over there too.